1. Technical Field of the Invention
The present invention relates to a zooming operation apparatus for use mainly in various kinds of cameras, and more particularly to a zooming operation apparatus of zoom lens specially provided with a rotary zooming operation ring.
2. Brief Description of Related Art
With recent practical utilization of cameras provided with automatic focusing function, zoom lenses capable of performing automatic focusing operation has been introducted. In the focusing mechanism by use of a zoom lens, the method of moving a first lens group which is most closely positioned to an object has heretofore been mainly adapted. However, in case the method is applied to a zoom lens capable of performing automatic focusing operation, a driving system needs to be provided for overall length of a body tube (lens barrel) since the driving force of a motor disposed in a camera body is transmitted to the first lens group thereby causing the body tube to become bulky.
On the other hand, in order to lighten the weight of the body tube and also to reduce its manufacturing cost, it has been tried to replace the metallic material used for the body tube with such material as synthetic resin which is light in weight and low in material cost. However, the material should be thick enough to insure its strength which causes the body tube to become bulky.
FIG. 1 shows a well-known zooming operation apparatus which is applied to a zoom lens capable of performing automatic focusing operation. It is arranged to firstly transmit the rotation of a zoom ring (a) held on an outer periphery (i) of a stationary barrel to a zoom cam ring (f). Then, the rotation of the zoom cam ring (f) is converted into a rectilinear movement of a first lens group (b) and a second lens group (e) respectively.
A focusing ring (g) which is a part of a focusing mechanism reaches the inside rear portion of outer periphery (i) of the stationary barrel, i.e. at the side of image plane to connect with a driving gear (j) ready for automatic focusing. The driving gear (j) is connected to a coupler (1) which is engaged with a coupler of driving system on the side of a camera body through a reduction gear (k).
However, the zoom cam ring (f) is rotated relative to the stationary barrel, and therefore, it is required to convert the rotation into rectilinear movement of the first lens group (b) and the second lens group (e). Accordingly, a straight groove (m) for a sleeve (h) of the stationary barrel and cam grooves (n),(o) which contact the groove (m) have to be provided in the zoom cam ring (f), and cam follower pins (p),(q) which engage with the straight groove (m) and the cam grooves (n),(o) are required.
Furthermore, lens holding frames for holding the first lens group (b) and the second lens group (e) need to be connected to the cam followers pins (p),(q) respectively at the inner peripheral side of the sleeve (h). Accordingly, the holding frames, sleeve (h), zoom cam ring (f), focusing ring (g), zoom ring (a) and the like are overlapped around an optical axis which leads to increasing the number of parts thereby causing the body tube to become bulky and the lens inevitably becomes large. It is therefore necessary to consider that the cam grooves (n),(o) and the cam follower pins (p),(q) do not interfere and affect each other, so that the degree of freedom is lowered in designing.